Evoked cortical potentials in patients with “isoelectric” EEGs

Abstract Visual and somatosensory potentials were recorded by electronic averaging of 500–1000 responses in 50 unconscious, artificially respirated patients without cortical activity above 2 μV in the EEG. The cerebral catastrophe was of extracerebral origin in 28 patients and intracerebral in 22. At the time of investigation 19 patients had cranial nerve reflexes and 31 did not. The electroretinogram (ERG) was recorded simultaneously with the occipital potential. The ERG was often picked up by the occipital lead and the record from the somatosensory scalp area was sometimes contaminated by nerve action potentials of extracerebral origin. 1. 1. When cranial nerve reflexes were present there were also visual or somatosensory evoked cortical responses. The evoked potentials were delayed, their shape was simple and the late components were absent. Cerebral angiography performed in 6 patients showed intracranial circulation in all. 2. 2. When cranial nerve reflexes were absent there were no somatosensory evoked cortical potentials and there were visual evoked responses in only one patient. Aorto-cervical angiography performed in 20 patients revealed no intracranial circulation in 19. The one patient with visual, but no somatosensory, responses had intracranial circulation in the carotid, but a block of circulation in the basilar artery. Thus, absence of both visual and somatosensory evoked responses is reliable evidence of brain death in unconscious, unresponsive patients.